1. Field of the Invention
This invention relates to footwear, and more particularly to a footwear to be used in rugged environment, having improved structural support and flexibility.
2. Description of Related Art
One of the main criteria in shoe design is to design a footwear that is sturdy enough to protect the wearer""s feet and yet flexible enough to provide for comfortable walking. This is particularly true for rugged footwear such as work boots, where comfort is often compromised in a design for a strong footwear that can withstand tough conditions.
The use of inserts in a footwear is well-known in the prior art. The purpose of many existing inserts, especially insoles, is for increasing comfort for the wearer by ways of providing additional cushioning and/or ventilation qualities. Many of the existing insoles are removable from the footwear for easy disposal or replacement. Since these insoles are removable items, they are generally not intended to provide structural support and strength to the footwear in which such insoles are used.
Indeed, very little prior art suggests the use of insoles as a structural chassis for providing increased structural support and strength of the footwear.
In U.S. Pat. No. 5,915,820, to Kraeuter et. al., a structural chassis made of a stiff, resilient material, such as vinyl or plastic, is disclosed. Further, notches of various length and width are placed in various portions of the chassis to provide a desired degree of stiffness and/or flexibility along the chassis. One of the unique features of the footwear disclosed in the Kraeuter patent is that the footwear does not have contiguous midsole and outsole. Further, the structural chassis is used to provide structure support for a footwear in areas without any outsole or midsole material. In other words, the structural chassis is the primary structural support of the footwear in those areas. The purpose of this combination of the structural chassis with non-contiguous midsole and outsole is to make a footwear that is flexible and light, and yet still provides certain structural support. The primary objective of the, Kraeuter patent is to eliminate the midsole and outsole, which normally span the entire length of the footwear, so that the weight of the footwear can be minimized. This invention is relevant to the design of footwear where light weight is a primary consideration, such as running or sports shoes. The Kraeuter patent discloses that the structural chassis is to be bonded to other layers of materials to form the sole of the footwear. Further, since the primary focus of the invention is to produce a light weight footwear for sports, it is not anticipated that the wearer will wear the footwear in extreme rugged conditions on a regular basis, for example in the case of a work boot, where strength and structural support are a primary concern.
One example of using an insole for providing increased structural support and strength to the footwear used .in rugged conditions, such as a work boot, can be found in a product brochure for Roadmate""s 2000 Collection. In the brochure, an insole using Texon material is described. The Texon insole described utilizes the HYTERLINK(trademark) Technology (Hyper Tension Release Link). The Texon insole utilizes a Texon board, which is a paper board. But instead of using the old-fashioned way of cementing (or gluing) a cloth welt around it, the HYTERLINK(trademark) technology utilizes PVC compounds injected into a mold that is in the shape of the insole. The insole is then injected onto the Texon board. On the insole, there is an inner welt, which is also formed by the injected PVC compound. The inner welt is sewn onto the insole, which provides lateral and torsional resistance, thus strengthening the footwear. There are also certain energy transfer bridges, again formed by the injected PVC compound, which serve to transfer shock and vibrations from the center to the side (the welt), onto the outsole and then to the ground.
The presence of the Texon insole provides enhanced lateral rigidity to the footwear, thus providing increased structural support and strength to the footwear. The reinforcement by the welt also strengthens the lateral support. However, as noted above, the Texon insole described is not a unitary structure. It is recognized that an insole construction made entirely of the existing PVC compounds would substantially decrease the flexibility of the footwear. In order to maintain some flexibility at various sections of the insole, especially the forefoot section, PVC material is removed or no PVC compound is injected for those sections. However, the absence of the PVC compound in those sections also decreases the efficacy of using the PVC compound to increase the strength of the footwear. Further, because of the addition of the Texon board, the Texon insole is heavier and not water proof, and tends not to return substantially to its original shape after it is bent. Also, the Texon board is susceptible to structural deterioration due to prolonged flexing. Further, the use of different materials, such as the PVC compounds and the Texon board, to make the Texon insole, also increases the manufacturing costs and decreases the production efficiency.
As indicated, commonly, ways of increasing structural support and strength of the footwear may compromise its flexibility. Thus, the construction of an insole used to provide increased structural support and strength of the footwear must take into account the materials used, their softness and their ability to provide structural support and strength to the footwear.
The present invention is directed to a sole construction including an insole of a unitary structure and made of a single flexible material for providing increased structural support and strength of the footwear while maintaining certain level of flexibility of the footwear. Unlike the prior art Texon board insole construction, the present invention makes use of only a unitary construction of a flexible material to manufacture the insole. A preferred material should be pliant or flexible but yet can provide the strength and structural support to the footwear in which the insole is used.
Instead of using materials of different softness for the various sections in the insole to facilitate bending of the footwear, openings are added to various locations in the insole to facilitate planar bending movement without significantly compromising the lateral rigidity of the insole. Such openings are commonly located in the forefoot section of the insole.
To increase structural support and strength to the footwear, the insole construction is fixedly secured to the footwear around the perimeter of the insole. In accordance with one embodiment of the present invention, the insole construction is stitched to the other layers in the footwear around the insole, for example using a welt.
Another embodiment of the invention is a footwear, constituting a combination of the insole as described, a midsole, and an outsole. In this embodiment, similar to the insole, the midsole also contains openings but such openings are extended through the entirety of the midsole""s surface, Similar to the openings in the insole, the openings in the midsole supplement and increase the flexibility of the footwear.